Method and device for detection of a UMTS signal

ABSTRACT

The present invention relates to a method (and corresponding device) of detecting a first signal in a received signal using a pattern, the received signal comprising at least one signal group, each signal group comprising a number of signal symbols, the pattern comprising at least one pattern group, each pattern group comprising at least a number of pattern symbols, wherein the method comprises the steps of for each signal group multiplying each signal symbol with a corresponding pattern symbol of a pattern group and deriving a sum of the products of multiplication, applying a weight factor of one or more weight factors to each sum giving a weighted sum, where said one or more weight factors are selected to preserve an orthogonality relation of said pattern symbols of the least one pattern group, and determining if a signal is detected or not based on said one or more weighted sums.

This patent application claims the benefit of priority from U.S.Provisional Patent Application Ser. No. 60/414,055 filed on Sep. 27,2002, and U.S. Provisional Patent Application Ser. No. 60/482,673 filedon Jun. 26, 2003. This application incorporates by reference the entiredisclosure of U.S. Provisional Patent Application Ser. Nos. 60/414,055and 60/482,673.

FIELD OF THE INVENTION

The present invention relates to a method and device for detection of asignal in a communications system.

BACKGROUND OF THE INVENTION

The detection of the Acquisition Indicator Channel (AICH) according to3rd generation partnership project (3GPP) specifications is part of therandom access procedure. The procedure can be described as follows. Inorder for a terminal or a user equipment (UE) to send a Random AccessChannel (RACH) message, it first needs to decode the Broadcast Channel(BCH) to find out what are the available RACH sub-channels, scramblingcodes, and signatures. The UE selects randomly one of the RACHsub-channels from the group its access class allows it to use. Thisimplies a restriction on when a RACH preamble can be sent. Then thesignature is selected randomly. There are sixteen signatures available,which means that sixteen UE can send at the same time. The downlinkpower level is then measured and the uplink power level is set withproper margin due to open loop inaccuracy. A 1 ms RACH preamble is sentwith the selected signature. The UE then listens for a confirmation fromthe base-station. The confirmation is sent through the AICH. In case noAICH is detected, the UE increases the preamble transmission power by astep given by the base station. The preamble is then retransmitted inthe next available access slot. When finally an AICH transmission fromthe base-station is detected in the UE, the UE transmits the 10 ms or 20ms message part of the RACH transmission.

A RAKE receiver is typically used in digital wireless communicationsystems to improve the performance of a CDMA (Code-Division MultipleAccess) receiver by utilizing signal energy carried by many multipathcomponents. In a RAKE receiver this is achieved by letting eachmultipath component be assigned a despreader whose reference copy of thespreading code is delayed equally to the path delay of the correspondingmultipath component. The outputs of the de-spreaders (fingers) are thencoherently combined to produce a symbol estimate. The RAKE receiver usesknowledge of the multipath delays and the values of the channel impulseresponse for all paths.

One prior art method of and device for signal detection simply uses asummation of the sent AICH symbols, which is less robust and does notprovide reliable detection, especially when a detector moves at arelatively high speed due to fading.

EP 1170880 discloses a radio base station device and radio communicationmethod that enables adaptive array antenna (AAA) reception by a RACH andAAA transmission by an AICH and reduced interference with other basestations.

However, this device and method does not provide reliable detection whenmoving at relatively high speed, since the problem of avoiding theeffects of fading that makes the signal strength vary is not addressed.Further weights are not derived. Instead an already known signal section(preamble section) of the RACH is used.

OBJECT AND SUMMARY OF THE INVENTION

An object of the present invention is to provide a complete method ofand a device usable for AICH detection and/or detection of other typesof signals.

A further object of the present invention is to provide a detectionmethod and a detection device that enables detection of an acquisitionsignal or another type of signal even when the physical detector ismoved at a relatively large velocity.

An additional object of the present invention is to provide a detectionmethod and a detection device having a more robust detection of asignal.

A further object of the present invention is to provide a threshold fordetection vs. no detection of an acquisition signal or another type ofsignal.

These objects, among others, are achieved by a method of detecting afirst signal in a received signal using a pattern, the received signalcomprising at least one signal group, each signal group comprising anumber of signal symbols, the pattern comprising at least one patterngroup, each pattern group comprising a number of pattern symbols,wherein the method comprises the steps of:

-   -   for each signal group multiplying each signal symbol with a        corresponding pattern symbol of a pattern group and deriving a        sum of the products of multiplication,    -   applying a weight factor of one or more weight factors to each        sum giving a weighted sum, where said one or more weight factors        are selected to preserve an orthogonality relation of said        pattern symbols of the at least one pattern group, and    -   determining if a signal is detected or not based on said one or        more weighted sums.

In this way, a complete method of reliable detection is provided.Further, a detection method is provided that enables robust detection ofan acquisition signal or another similar type of signal even when thephysical detector is moved at a relatively large velocity, sinceorthogonality of the pattern is preserved due to the applied weightfactors, even when fading makes the signal strength vary within theduration of the signature pattern that may cause false detections.

In one embodiment, the step of determining if a signal is detected ornot comprises

-   -   adding said one or more weighted sums giving a first result, and    -   comparing said first result with a detection threshold in order        to determine whether said signal is detected or not.

In one embodiment, the detection threshold is derived based on a signalto interference ratio of a common pilot channel (CPICH).

In an alternative embodiment, the detection threshold is derived basedon a signal to interference ratio, where the interference is estimatedon the basis of symbols of the received signal (y) that should be zero.In this way, a simple estimation of the interference may be obtained,since the specific value of the symbols that is known to be zero arisesdue to noise/interference.

In one embodiment, the detection threshold is derived based on a falsedetection rate factor and a standard deviation of the interference ofthe received signal.

In one embodiment, the one or more weight factors are derived on thebasis of a signal to interference ratio (SIR) calculated for a commonpilot channel (CPICH).

In one embodiment, the signal to interference ratio (SIR) calculated fora common pilot channel (CPICH) is dependent on an estimate of theinterference for a given finger and a given group, where said methodfurther comprises the step of:

-   -   averaging the estimate of the interference over a predetermined        number of groups (j) before deriving said one or more weight        factors on the basis of the signal to interference ratio (SIR)        calculated for the common pilot channel (CPICH).

This reduces the uncertainty of the interference estimates enabling abetter detection.

Preferably, the first signal is an acquisition indicator channel (AICH)signal or a collision detection/channel assignment indicator channel(CD/CA-ICH).

In one embodiment, the received signal is an estimated signal derived onthe basis of one or more weighted channel estimates and of de-spreadsymbols from a RAKE, wherein the one or more weighted channel estimatesare based on a common pilot channel (CPICH).

In a preferred embodiment, the received signal (y) comprises two orthree signal groups and the pattern (ŝ) comprises at least two or threepattern groups. The use of two or more groups and thereby two or moreweight factors (x) enables a correction of the otherwise destroyedorthogonality and thereby elimination of false and/or unreliabledetection at even higher velocities.

The invention also relates to a device for detecting a first signal in areceived signal using a pattern, the received signal comprising at leastone signal group, each signal group comprising a number of signalsymbols, the pattern comprising at least one pattern group, each patterngroup comprising at least a number of pattern symbols, wherein thedevice comprises:

-   -   means adapted to for each signal group to multiply each signal        symbol with a corresponding pattern symbol of a pattern group        and to derive a sum of the products of multiplication,    -   means for applying a weight factor of one or more weight factors        to each sum giving a weighted sum, where said one or more weight        factors are selected to preserve an orthogonality relation of        said pattern symbols of the at least one pattern group, and    -   means for determining if a signal is detected or not based on        said one or more weighted sums.

In one embodiment, the means for determining if a signal is detected ornot further comprises

-   -   a summation circuit for adding said one or more weighted sums        giving a first result, and    -   detection means for comparing said first result with a detection        threshold in order to determine whether said signal is detected        or not.

In one embodiment, the device further comprises processing means forderiving said detection threshold based on a signal to interferenceratio of a common pilot channel.

In one embodiment, the device further comprises processing means forderiving said detection threshold based on a false detection rate factorand a standard deviation of the interference of the received signal.

In an alternative embodiment, the device further comprises processingmeans for deriving said detection threshold on the basis of a signal tointerference ratio and for estimating the interference on the basis ofsymbols of the received signal that should be zero.

In one embodiment, the device further comprises processing means forderiving one or more weight factors on the basis of a signal tointerference ratio calculated for a common pilot channel (CPICH).

In one embodiment, the signal to interference ratio (SIR) calculated fora common pilot channel (CPICH) is dependent on an estimate of theinterference for a given finger and a given group, and said processingmeans is further adapted to:

-   -   average the estimate of the interference over a predetermined        number of groups before deriving said one or more weight factors        on the basis of the signal to interference ratio (SIR)        calculated for the common pilot channel (CPICH).

In one embodiment, the first signal is an acquisition indicator channel(AICH) signal or a collision detection/channel assignment indicatorchannel (CD/CA-ICH).

In one embodiment, the device further comprises a combiner circuit forderiving said received signal as an estimated signal derived on thebasis of one or more weighted channel estimates and of de-spread symbolsfrom a RAKE, wherein the one or more weighted channel estimates is basedon a common pilot channel (CPICH).

In one embodiment, the received signal comprises two or three signalgroups and that the pattern comprises at least two or three patterngroups.

Further, the invention also relates to a computer readable medium havingstored thereon instructions for causing one or more processing units toexecute the method according to the present invention.

The signal detection is essentially a correlation. Judging from the sizeof the correlation output we determine if we have detected a signal ornot. This requires a threshold to distinguish detection from nodetection, which is part of the present invention.

The present invention splits up a received signal into parts, assigns aweight factor to each part, sums the weighted parts and uses a thresholdin order to determine whether a given signal is detected or not.

Embodiments of the invention could advantageously be part of a basebandchip in UMTS terminals. Generally, the invention may be useful in allmarkets or products relating to UMTS terminals, user equipments, mobilephones, smart phones, PDA's, etc.

Although, AICH detection is used throughout this specification, theinvention may also be used for detecting other types of signals withsimilar properties. As one example of such a signal is the CollisionDetection/Channel Assignment Indicator Channel (CD/CA-ICH) according tothe 3rd generation partnership project (3GPP) specifications. CD/CA-ICHwas also previously denoted CD-ICH.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic block diagram of a general embodiment ofa detection circuit according to the present invention;

FIG. 2 a illustrates a more detailed schematic block diagram of anaccumulator circuit according to one embodiment of the presentinvention;

FIG. 2 b illustrates a more detailed schematic block diagram of anaccumulator circuit according to a preferred embodiment of the presentinvention;

FIG. 3 illustrates a schematic block diagram of an embodiment of adetection circuit according to the present invention for detection ofthe Acquisition Indicator Channel (AICH);

FIG. 4 illustrates a schematic flow chart of an embodiment of the methodaccording to the present invention;

FIG. 5 illustrates a number of AICH signature patterns according to 3GGPTS 25.211 V4.3.0 (2201-12).

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a schematic block diagram of a general embodiment ofa detection circuit according to the present invention. A detectioncircuit (100) for detecting a specific signal in a symbol sequence isshown, where the circuit (100) comprises an accumulator circuit (102)and a processing unit (103), the processing unit (103) e.g. comprisingat least one general purpose and/or at least one special purposeprocessing unit and/or at least one digital signal processor (DSP).

The accumulator circuit (102) receives a signal (y) via a connection(113), where the signal (y) comprises the symbols on which signaldetection is to be performed and further receives a signal via anotherconnection (114) from the DSP (103), where this signal comprises asequence, signature, pattern or the like (ŝ) (henceforth only denotedpattern), comprising a number of symbols. The symbols of the signal (y)may be grouped in one or more groups (i.e. J groups, where J is apositive integer being equal to or larger than 1), where each groupcomprises a number of symbols and preferably is processed independentlyof the other groups, if any, of the signal (y). Different groups maye.g. comprise a different number of symbols, Alternatively, all thegroups may comprise the same number of symbols. Together, all the groupscomprise L symbols, e.g. forming the symbols of a signal access slot,where L is at positive integer.

The pattern (ŝ) preferably comprises at least as many symbols as thenumber of symbols of the signal (y), i.e. at least L symbols. Thepattern (ŝ) may also be grouped in one or more groups comprising a sameor a different number of symbols. Preferably, the pattern (ŝ) is groupedor split up in as many groups as are the symbols of the signal (y) inwhich detection of a signal is to be performed, i.e. J groups andpreferably a given group of the pattern (ŝ) is used in connection with agiven group of the signal (y).

In one embodiment, the symbols of the signal (y) are organised in twoblocks, i.e. J=2, where the first black comprises 10 symbols and thesecond block comprises 6 symbols. In this embodiment, the pattern (ŝ)would comprise 16 symbols, and would preferably be split into two groups(ŝ⁽¹⁾ and ŝ⁽²⁾), where (ŝ⁽¹⁾) comprises 10 symbols and (ŝ⁽²⁾) comprises6 symbols. Alternatively, other groupings of the signal (y) and/or thepattern (ŝ) may be used.

Preferably, a number of weight factors (x), are also received by theaccumulator circuit (102) from the processing unit/DSP (103) viaconnection (114) or alternatively from another unit and/or via anotherconnection (not shown). Preferably, one weight factor (x_(j)) for eachsymbol group is received, i.e. x_(j), j∈1, . . . , J. In one embodiment,the weight factor(s) (x) are generated on the basis of a signal tointerference ratio (SIR), e.g. as explained later in connection withFIG. 3. The purpose of the weight factors is to maintain orthogonalityof the symbol groups e.g. in order to compensate for the presence offading, which otherwise easily destroys the orthogonality and thereby areliable detection of the signal.

In the accumulator circuit (102) each symbol of the signal (y) ismultiplied with a corresponding symbol from the pattern (ŝ). A weightfactor (x) is applied to each of the resulting L products after which asum of the weighted products is generated resulting in a result denotedfirst result. Different or same weight factors (x) may be applied to theresulting products. Hence

${{{First}\mspace{14mu}{result}} = {\sum\limits_{l = 1}^{L}{x_{l}y_{l}{\hat{s}}_{l}}}},$where l enumerates the symbols of the signal (y) and the symbols of thepattern (ŝ).

Preferably, the accumulator circuit (102) operates on groups of symbolsinstead of directly on specific symbols where each symbol of a givengroup is applied the same weight factor (x_(j)), i.e. the symbols of agiven group of the signal (y) and the symbols of a given group of thepattern (ŝ) are multiplied preferably on a symbol-level (i.e. the firstsymbol of the given signal group is multiplied with the first symbol ofthe given pattern group, etc.) and where the resulting products areadded in order to generate a sum after which a weight factor (x_(j)) isapplied to the resulting sum. If both the group of the signal (y) andthe pattern (ŝ) are in vector-form, this corresponds to taking thescalar product and applying a weight factor. After this has been done,the resulting weighted sums for each block are added to give the firstresult. Hence

${{First}\mspace{14mu}{result}} = {\sum\limits_{j = 1}^{J}{x_{j}{\sum\limits_{k = 1}^{K}{y_{k}^{(j)}{\hat{s}}_{k}^{(j)}}}}}$if every block of both the signal (y) and the pattern (ŝ) comprises Ksymbols (or if there are K symbols in the largest block(s) and theremaining other blocks have zeroes inserted to give them a size of Ksymbols).

In the embodiment, where the symbols of the signal (y) is organised intwo blocks, i.e. J=2, where both the first block of the signal (y) andthe first part of the pattern (ŝ) comprises 10 symbols and where thesecond block of the signal (y) and the second part of the pattern (ŝ)comprises 6 symbols, the first result would be:

${{First}\mspace{14mu}{result}} = {{x_{1}{\sum\limits_{k = 1}^{10}{y_{k}^{(1)}{\hat{s}}_{k}^{(1)}}}} + {x_{2}{\sum\limits_{k = 1}^{6}{y_{k}^{(2)}{\hat{s}}_{k}^{(2)}}}}}$where y_(k) ^((j)) is the k′th symbol in block j for the signal (y) andŝ_(k) ^((j)) is the k′th symbol in block j for the pattern (ŝ).

The first result is then compared with a threshold (τ) received in theaccumulator circuit (102) from the DSP (103), via connection (114) oralternatively from another unit and/or via another connection (notshown), in order to determine whether the specific signal is detected ornot. The result of the detection is preferably sent from the accumulatorcircuit (102) via a connection (115) to the DSP, or alternatively toanother unit (not shown), for further use, processing, etc.

In one embodiment, the detection threshold (τ) is dependent on aprobability for false detections (FAR) and the resulting FAR-dependentthreshold is denoted τ_(FAR) in the following.

The function of the units of the detection circuit (100) may be modifieddepending on the characteristics of the signal (y) on which signaldetection is to be performed. As an example, the function of the unitsmay be modified to take into account the different fingers (f) in a RAKEreceiver, each corresponding to a path along which the signal (y)travels between the transmitter and the receiving terminal. Thiscomplicates the factors involved, but the above mentioned principle isthe same. This is explained in greater detail in connection with FIG. 3where detection of an Acquisition Indicator Channel (AICH) according to3rd generation partnership project (3GPP) specifications is described.

FIG. 2 a illustrates a more detailed schematic block diagram of anaccumulator circuit according to one embodiment of the presentinvention. An accumulator circuit (as shown in FIG. 1) for detection ofa signal is shown. In this exemplary embodiment, both the signal (y), onwhich detection is to be performed, and the pattern (ŝ) are arranged intwo groups (y⁽¹⁾), (y⁽²⁾) and (ŝ⁽¹⁾), (ŝ⁽²⁾), respectively. The pattern(ŝ) is received via connection (114) from a processing unit, DSP or thelike (not shown) and is received in the two groups (ŝ⁽¹⁾, ŝ⁽²⁾) or splitinto these by the accumulator circuit (102). Further, the signal (y) isreceived via connection (113) in the two groups (y⁽¹⁾, y⁽²⁾) or splitinto these by the accumulator circuit (102). The first group of both thesignal (y⁽¹⁾) and the pattern (ŝ⁽¹⁾) are received by a first accumulatorcircuit/function (201 a), that multiplies each symbol of (y⁽¹⁾) with acorresponding symbol of (ŝ⁽¹⁾). After multiplication, the resultingsymbol products (y⁽¹⁾ŝ⁽¹⁾) are added together resulting in a first sum(Σ₁).

Likewise, the second group of both the signal (y⁽²⁾) and the pattern(ŝ⁽²⁾) are received by a second accumulator circuit/function (201 b),that multiplies each symbol of (y⁽²⁾) with a corresponding symbol of(ŝ⁽²⁾), and adds the products together resulting in a second sum (Σ₂).

A first weight factor (x₁) (received via connection (114) from theprocessing unit/DSP) is applied to the first sum (Σ₁) by a firstmultiplication circuit/function (202 a).

In the same way, a second weight factor (x₂) (also received from theprocessing unit/DSP (103)) is multiplied with the second sum (Σ₂) by asecond multiplication circuit/function (202 b).

An adding circuit/function (203) adds the two weighted sums together andthe result of this addition, i.e. the first result, (x₁ Σ₁+x₂ Σ₂) isused by a decision circuit/function (204) to determine whether a givensignal is detected or not.

In one embodiment, the decision circuit/function (204) compares thefirst result with a threshold (τ, τ_(FAR)) in order to determine whethera specific signal is detected or not.

The symbols are weighted by the weight factors (x₁, x₂) in order tomitigate the influence of fading over an access slot, the access slotcomprising all the groups.

In alternative embodiments, the accumulator circuit (102) may comprise asingle accumulator or more than two accumulators corresponding to theones shown (201 a and 201 b), i.e. J accumulators. In anotheralternative embodiment, the accumulator circuit (102) comprises only asingle accumulator processing a group at a time out of the J groups.Such an embodiment is shown and explained in connection with FIG. 2 band has the advantage of reduced hardware complexity.

The use of two (or more) groups is useful if the terminal is moving at ahigh velocity, since fading could destroy the orthogonality of thepattern (ŝ) if only a single group was used for the entire signal (y)and pattern (ŝ). J=1 could be sufficient for relatively smallervelocities of the terminal, while J=2 or J=3 (or under certainsituations even higher) would be required for reliable detection athigher velocity.

FIG. 2 b illustrates a more detailed schematic block diagram of anaccumulator circuit according to a preferred embodiment of the presentinvention. An accumulator circuit (as shown in FIG. 1) for detection ofa signal is illustrated. In this exemplary embodiment, the accumulatorcircuit (102) function on a group basis in the sense that a group isprocessed at a time, i.e. in ‘serial’ as opposed to in ‘parallel’ as theembodiment in FIG. 2 a. The accumulator circuit (102) comprises anaccumulator circuit/function (201) that receives the symbols from agiven group (y^((j))) of the signal (y) via connection (113) and thesymbols from a given group (ŝ^((j))) of the pattern (ŝ) via connection(114) from a processing unit, DSP or the like (not shown). Theaccumulator circuit/function (201) multiplies each signal symbol of thegiven group (y^((j))) with a corresponding pattern symbol of the givengroup (ŝ^((j))). After multiplication, the resulting symbol products(y^((j))ŝ^((j))) are added together resulting in a sum (Σ_(j)).

A given weight factor (x_(j)) for the given group (received viaconnection (114) e.g. from the processing unit/DSP) is applied to thesum (Σ_(j)) by a multiplication circuit/function (202) giving a weightedsum (x_(j) Σ_(j)). The given weighted sum (x_(j) Σ_(j)) may be stored ina suitable memory (not shown) until all J groups have been processed.The given weight factor (x_(j)) may be pre-defined or generated on thebasis of the signal (y) and/or the pattern ŝ, e.g. as explained inconnection with FIG. 3 for the detection of an AICH signal.

After the given group j has been processed, the next group (if any) isprocessed in a similar manner until J groups have been processed and acorresponding weighted sum (x_(j) Σ_(j)) for each group have beenderived, after which an adding circuit/function (203) adds the weightedsums together. The result of this addition, i.e. the first result, (x₁Σ₁+ . . . +x_(J) Σ_(J)) is used by a decision circuit/function (204) todetermine whether a given signal is detected or not. In one embodiment,the decision circuit/function (204) compares the first result with athreshold (τ, τ_(FAR)) in order to determine whether a specific signalis detected or not. The adding circuit/function (203) may also add thegenerated weighted sums accumulatively, i.e. adding a generated weightedsum to the previous generated weighted sum(s) before the next weightedsum is derived, as this may save storage.

This embodiment uses less hardware than the one shown in FIG. 2 a.Groups of both the signal (y) and the pattern (ŝ) may be received andstored (e.g. together with intermediate results) in one or more buffers,memory circuits, etc. (not shown) while a given group of both the signal(y) and the pattern (ŝ) is processed.

If the signal (y) is time dependent, i.e. one or more groups areavailable before others, as often is the case for a communicationsrelated signal, the drawback of not being able to process groups inparallel is very small, negligible or non-existent.

FIG. 3 illustrates a schematic block diagram of an embodiment of adetection circuit according to the present invention for detection of anAcquisition Indicator Channel (AICH) according to 3rd generationpartnership project (3GPP) specifications. Shown is a detection circuit(100) comprising a combiner circuit (101), an accumulator (102) and aprocessing unit (103), the processing unit (103) e.g. comprising atleast one a general purpose and/or at least one special purposeprocessing unit and/or at least one digital signal processor (DSP).

The accumulator (102) corresponds to the one shown and explained inconnection with FIGS. 1 and 2 and the processing unit (103) correspondsto the one shown and explained in connection with FIG. 1.

The combiner (101) is connected to receive a signal via connection (111)from a RAKE and to receive a signal via connection (112) from theprocessing unit (103). The combiner (101) outputs a signal viaconnection (113) to the accumulator (102), which further receives asignal via connection (114) from the processing unit (103) and providesanother signal via connection (115) to the processing unit (103).

Typically, the Acquisition Indicator Channel (AICH) according to the 3rdgeneration partnership project (3GPP) specifications is sent using aspreading factor of 256. A total of 16 symbols are sent during an accessslot, which corresponds to 10 symbols in one group and 6 symbols in thenext group. The duration of an access slot equals two groups. The realand imaginary parts of the sent symbols are equal. Up to 16 differentsymbol combinations can be sent. The different symbol combinations areorthogonal and are usually called signature patterns; see e.g. 3GPP, 3rdgeneration partnership project specifications, 3GPP TS 25.133, V3.3.0,June 2001. (incorporated herein by reference) and FIG. 5.

More specifically in connection to detection of the AcquisitionIndicator Channel (AICH) according to 3GPP, 3rd generation partnershipproject specifications, the combiner (101) receives an AICH symbolsignal via connection (111) comprising de-spread AICH symbols from theRAKE (not shown) and a signal (112) comprising weighted channelestimates (w), preferably based on the Common Pilot Channel (CPICH),from the processing unit/the DSP (103).

In the following, the index j enumerate groups of K symbols, where j=1,. . . , J and J is the smallest integer such that J×K≧16, where thenumber 16 is due to that there are 16 symbols in an access slot.

The despread AICH symbols of the AICH symbol signal are denoted y_(k,f)^((AICH)), where the index k enumerates the received symbols of a givengroup comprising K symbols and the index f∈[1, . . . , F] enumerates themulti-path delays or RAKE fingers. The received AICH symbols are afterdespreading given by

$y_{k,f}^{({AICH})} = {{h_{k,f}{\sum\limits_{\hat{s} = 0}^{15}{\frac{\alpha_{\hat{s}}}{\sqrt{2}}{AI}_{\hat{s}}b_{\hat{s},k}}}} + n_{k,f}}$where the index k enumerates the received symbols and the index fenumerates the multi-path delays or fingers, the radio channel is givenby h_(k,f), α_(ŝ) ² denotes the transmitted symbol energy of AICHsignature ŝ, and the complex numbers b_(ŝ,k)=±(1+i) are the sent AICHsymbols. The acquisition indicator for signature ŝ is given by AI_(ŝ)and equals −1, 0 or 1. The interference is modelled by n_(k,f). Se FIG.5 for the values of b_(ŝ,k) and ŝ, where ŝ=s andb_(ŝ,k)=b_(s,2k)+ib_(s,2k+1) since b_(ŝ,k) is complex numbers andb_(s,n) in FIG. 5 gives the real and imaginary parts of these complexnumbers.

If AI_(ŝ)>0, the base station acknowledges that it is aware of theterminal or the user equipment and a RACH can be sent. If AI_(ŝ)=0, thebase station could not hear the terminal or the user equipment. Hence,the power of the preamble is increased before a new transmission istried. If AI_(ŝ)<0, the base station heard the terminal or the userequipment, but instructs it to not send a RACH message.

For the CPICH, the received signal (not shown) after despreading isgiven by (using the approximation that the AICH and CPICH interferencesare equal, which is reasonable since both transport channels have thesame spreading factor)

$y_{k,f}^{({CPICH})} = {{h_{k,f}\frac{\alpha_{CPICH}}{\sqrt{2}}c} + n_{k,f}}$where c is the complex number (1+i), the radio channel is given byh_(k,f), the interference is modelled by n_(k,f) and α_(CPICH) squareddenotes the transmitted symbol energy for the CPICH signal.

In a preferred embodiment, statistics on the interference are estimatedin the following on the basis on the CPICH, since in practice there arenot enough AICH data samples. In an alternative embodiment, anestimation of the interference could be based on the fact that the lastfour symbols in an access slot are zero and hence y_(k,f) ^((AICH)),k=16, 17, 18, 19 equals the interference. In this way, the detectionthreshold (τ,τ_(FAR)) may derived based on a signal to interferenceratio, where the interference is estimated on the basis of symbols ofthe received signal (y) that should be zero.

The weighted channel estimates (based on the CPICH) are denoted w_(k,f)for symbol k and finger f. The weighted channel estimates (w_(k,f)) maybe derived on the basis of the channel estimate for each finger (f)weighted with its interference (see e.g. J. Proakis, Digitalcommunications, McGraw-Hill Int. Edition, 3rd Ed, 1995 (incorporatedherein by reference) for further details), i.e. the weighted channelestimates (w_(k,f)) may be given by (assuming that the radio channelh_(k,f) is constant over K CPICH symbols)

${w_{k,f} = {w_{f}^{(j)} = {\frac{{\overset{\_}{h}}_{f}^{(j)}}{N_{f}^{(j)}} \approx \frac{\alpha_{CPICH}h_{k,f}}{\sqrt{2}\sigma_{f}^{2}}}}};$k = 1 + (j − 1)K, …  , jK; j = 1, …  , Jwhere h _(f) ^((j)) is a radio channel estimate over group j, and N_(f)^((j)) is an estimate of the interference for finger f and group j,σ_(f) ² is the variance of the interference.

As mentioned, the weighted channel estimates (w) are preferably derivedin the processing unit/DSP (103) and supplied to the combiner (101).

A summation is done in the combiner (101) over the fingers f for y_(k,f)^((AICH)) multiplied by the complex conjugate of the weighted channelestimates, i.e.

${\sum\limits_{f = 1}^{F}{y_{k,f}^{({AICH})}w_{k,f}^{*}}},$which is an estimate of the sent AICH symbol(s) and is the output signal(113) of the combiner (101). The estimate of the sent AICH symbol(s)would in the context of FIGS. 1 and 2 correspond to the signal (y). Upuntil now, the procedure is identical to what would have been done for adedicated channel according to the 3rd generation partnership project(3GPP) specifications.

If the number of symbols in each group is small it is useful to averageN_(f) ^((j)) over a relatively small number of groups before the channelestimates are scaled with its inverse, i.e. before deriving the weightedchannel estimates (w_(k,f)). This reduces the uncertainty of theinterference estimates enabling a better detection.

The accumulator (102) receives the symbol(s)

$\sum\limits_{f = 1}^{F}{y_{k,f}^{({AICH})}w_{k,f}^{*}}$via connection (113) from the combiner and receives from the processingunit/DSP (103) via connection (114) which pattern ŝ to use, whereb_(ŝ,k) is the k′th symbol in the desired signature pattern ŝ. Thespecific pattern ŝ to use is picked randomly as specified in the 3GPPspecification.

A first accumulator in the accumulator circuit (102) (corresponds to thegeneral circuit/function 201 a and 201 b in FIGS. 2 a and 2 b)multiplies the combiner symbols in the first group with thecorresponding signature pattern symbols b_(ŝ,k) (corresponding to ŝ⁽¹⁾and ŝ^((j)) in FIGS. 2 a and 2 b, respectively) and adds the resultingproducts giving a first sum (Σ₁ and Σ_(j) in FIGS. 2 a and 2 b,respectively). Then the remaining 6 symbols (for this particular exampleof AICH detection) in the second group are multiplied with thecorresponding signature pattern symbols (corresponding to ŝ⁽²⁾ andŝ^((j)) in FIGS. 2 a and 2 b, respectively), the resulting productssummed giving a second sum (Σ₂ and Σ_(j) in FIGS. 2 a and 2 b,respectively) in a second or the same accumulator (corresponding to thecircuit/function 201 b in FIG. 2 a or to the circuit/function (201) inFIG. 2 b, respectively).

In this way, the de-rotated symbols are multiplied with b_(ŝ,k) (lettingb_(ŝ,k)=0 if the index k>16 for this particular example) and the resultsare added together in groups of K symbols, i.e.

$A_{j} = {\Sigma_{j} = {{Re}{\sum\limits_{k = {1 + {{({j - 1})}K}}}^{jK}{b_{\hat{s},k}^{*}{\sum\limits_{f = 1}^{F}{y_{k,f}^{({AICH})}w_{k,f}^{*}}}}}}}$

A number of weight factors Ĉ_(j), j=1, . . . J (corresponding to 1/x₁and 1/x₂ of the embodiment shown in FIG. 2 a where J=2 or 1/x_(j) of theembodiment shown in FIG. 2 b where j∈(1, . . . , J; J≧1)) are receivedby the accumulator (102) via connection (114) from the processingunit/DSP (103) and the result from the first accumulator, i.e. the firstsum, is multiplied with the inverse of the first weight factor Ĉ₁ whilethe result from the second or the same accumulator, i.e. the second sum,is multiplied with the inverse of the second weight factor Ĉ₂.Preferably, the weight factors are derived from the signal tointerference ratio (SIR), calculated for the CPICH.

${\hat{C}}_{j} = {\frac{1}{x_{j}} = {{Re}{\sum\limits_{f = 1}^{F}{\left( w_{k,j} \right)^{*}{\overset{\_}{h}}_{f}^{(j)}}}}}$

After the weight factors have been applied to the sums, the J resultingweighted sums are added giving a first result, i.e.

${{First}\mspace{14mu}{result}} = {\sum\limits_{j = 1}^{J}\frac{A_{j}}{{\hat{C}}_{j}}}$

In a preferred embodiment, the first result is given by

${{First}\mspace{14mu}{result}} = {\sum\limits_{j = 1}^{J}{C\frac{A_{j}}{{\hat{C}}_{j}}}}$where C is a variable aimed at making the division A_(j)/Ĉ_(j) moretractable. As an example C=max{Ĉ₁, . . . , Ĉ_(J)}, as this reduces thecomputational complexity, especially important in equipment, devices,etc. with a limited power supply.

In effect, the accumulated values A_(j) are scaled with thecorresponding CPICH signal to interference ratio (SIR) (as approximatedby Ĉ_(j)), in order to remove the effect of the fading that wouldotherwise destroy the orthogonality of the patterns ŝ.

The determination of whether a signal is detected or not is based onsaid first result.

Preferably, the first result is compared to a threshold τ_(FAR) providedby the processing unit/DSP (103) and on the basis of the comparison adecision of the acquisition indicator AI_(ŝ) is made. In one embodiment,this decision is done on the basis of the SIR for the CPICH and isprovided to the processing unit/DSP (103) for further use.

In this way the acquisition indicator AI_(ŝ) is given by

${AI}_{\hat{s}} = \left\{ \begin{matrix}{{- 1},} & {{{\sum\limits_{j = 1}^{J}{C\frac{A_{j}}{{\hat{C}}_{j}}}} < {- \tau_{FAR}}},} \\{1,} & {{{\sum\limits_{j = 1}^{J}{C\frac{A_{j}}{{\hat{C}}_{j}}}} > {- \tau_{FAR}}},} \\{0,} & {else}\end{matrix} \right.$

As mentioned earlier, the reason for using two or more groups in theaccumulator circuit (102) is because a varying signal strength and/orfading destroys the orthogonality of the signature patterns ŝ, that maycause false detections. The use of two or more groups and thereby two ormore weight factors (x) enable a correction of the otherwise destroyedorthogonality and thereby elimination of false and/or unreliabledetection.

In this way, a complete method of and a device usable for AICH detectionare provided. Further, a detection method and detection device areprovided that enables robust detection of an acquisition signal oranother similar type of signal even when the physical detector is movedat a relatively large velocity, since orthogonality in the pattern ispreserved, even when fading makes the signal strength vary within theduration of the signature pattern.

In a preferred embodiment, the threshold τ_(FAR) is generated on thebasis of the inverse of the SIR for the CPICH for symbol group j, i.e.

${ISR}_{j}^{({CPICH})} = \frac{1}{\sum\limits_{f = 1}^{F}\frac{\left| h_{f}^{(j)} \right|^{2}}{N_{f}^{(j)}}}$where N_(f) ^((j)) estimates the interference for symbol block j andmulti-path delay f.

Further, filtered values are derivedISR _(filt,j) ^((CPICH))=(1−λ_(ISR))ISR _(filt,j−1) ^((CPICH))+λ_(ISR)ISR _(j) ^((CPICH))where λ_(ISR) is a predefined parameter e.g. set to 1/16.

Take

σ_(ε)=√{square root over (8ISR_(filt,J) ^((CPICH)))}, here ISR_(filt,J)^((CPICH)) represents the last filtered value in the access slot, andτ_(FAR)=Cl_(FAR)σ_(ε)where l_(FAR) is a predetermined false detection rate factor, then theacquisition indicator is given by the above mentioned expression.

Here σ_(ε) estimates the standard deviation of the interference of thesignal given by the above-mentioned first result. Given that theinterference can be modelled as Gaussian noise, l_(FAR) may be selecteddependent on a specific value for the probability for false detections(FAR), e.g. l_(FAR)=1.6 for FAR=0.1, l_(FAR)=2.2 for FAR=0.03 orl_(FAR)=2.6 for FAR=0.01. In practice, some fine tuning will typicallyalways be needed, since the noise is not perfectly Gaussian.

FIG. 4 illustrates a schematic flow chart of an embodiment of the methodaccording to the present invention. The method starts and is initialisedat step (400). At step (401), it is determined which pattern (ŝ) to use.The specific pattern ŝ to use is picked randomly as specified in the3GPP specification.

At step (402), the symbols from a given group (y^((j))) of the signal(y) and the symbols from a given group (ŝ^((j))) of the pattern (ŝ) ismultiplied as described earlier.

At step (403), the resulting symbol products (y^((j))ŝ^((j))) are addedtogether resulting in a sum (Σ_(j)).

At step (404), a given weight factor (x_(j)) for the given group isapplied to the sum (Σ_(j)) by a multiplication circuit/function (202)giving a weighted sum (x_(j) Σ_(j)). The weight factor may bepre-determined or derived as described elsewhere.

The steps (402, 403, and 404) may e.g. be performed in parallel ondifferent groups as described in connection with FIG. 2 a or in turn asdescribed in connection with FIG. 2 b.

After every group has been processed and a corresponding weighted sum(x_(j) Σ_(j)) for each group has been derived, the weighted sums (ifmore than 1) are added at step (405) giving a first result. If only asingle weighted sum is generated the first result is that sum.Alternatively, the sum of the weighted sums may be generated gradually,e.g. initialising a variable to the first generated weighted sum andthen adding to next generated weighted sums to this variable as they aregenerated.

At step (406), the first result is used to determine whether a givensignal is detected or not. In one embodiment, a simple comparison ismade between the first result and a threshold (τ,τ_(FAR)) in order todetermine whether a specific signal is detected or not, as describedelsewhere.

FIG. 5 illustrates a number of AICH signature patterns according to 3GGPTS 25.211 V4.3.0 (2201-12). In this figure a number of specific values(b_(s,n); n∈0, . . . , 31) are listed for a number of signatures (s=ŝ;s∈0, . . . , 15) according to the 3GGP specification, whereb_(ŝ,k)=b_(s,2k)+ib_(s,2k+1).

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps or components but does not preclude thepresence or addition of one or more other features, integers, steps,components or groups thereof.

Although preferred embodiments of the present invention have beendescribed and shown, the invention is not restricted to them, but mayalso be embodied in other ways within the scope of the subject matterdefined in the following claims.

1. A method of detecting, by a detection circuit of a receiver, a firstsignal in a received signal (y) using a pattern (ŝ), the received signal(y) comprising at least one signal group (y⁽¹⁾, . . . , y^((J))), eachsignal group comprising a number (K) of signal symbols, the pattern (ŝ)comprising at least one pattern group (ŝ⁽¹⁾, . . . , ŝ^((J))), eachpattern group comprising at least a number (K) of pattern symbols, themethod comprising: multiplying, in an accumulator circuit, for each ofsaid at least one signal group (y⁽¹⁾, . . . , y^((J))), each signalsymbol with a corresponding pattern symbol of said at least one patterngroup (ŝ⁽¹⁾, . . . , ŝ^((J))) and deriving a sum (Σ₁, . . . , Σ_(J);A_(j)) of the products of multiplication, receiving one or more weightfactors (x₁, . . . , x_(J); Ĉ_(j)) by the accumulator circuit from aprocessing unit/DSP; applying a weight factor (x₁, . . . , x_(J); Ĉ_(J))of one or more weight factors (x₁, . . . , x_(J); Ĉ_(j)) by theaccumulator circuit to each sum (Σ₁, . . . , Σ_(J); A_(j)) giving aweighted sum (x₁Σ₁, . . . , x_(j)Σ_(J); A_(j)/Ĉ_(j)), wherein said oneor more weight factors (x₁, . . . , x_(j); Ĉ_(j)) are selected topreserve an orthogonality relation of said pattern symbols of the atleast one pattern group; and determining if a signal is detected or notbased on said one or more weighted sums (x₁Σ₁, . . . , x_(j)Σ_(J);A_(j)/Ĉ_(j)).
 2. The method according to claim 1, wherein said step ofdetermining if a signal is detected by a detection circuit of areceiver, comprises: adding said one or more weighted sums (x₁Σ₁, . . ., x_(j)Σ_(J); A_(j)/Ĉ_(j)) giving a first result (x₁Σ₁,+ . . . ,+x_(j)Σ_(J); A_(j)/Ĉ_(j); Σ_(j=1)CA_(j)/Ĉ_(j)); and comparing, by theaccumulator circuit, said first result with a detection threshold (τ,τ_(FAR)) received from the processing unit/DSP in order to determinewhether said signal is detected or not.
 3. The method according to claim2, wherein said detection threshold (τ, τ_(FAR)) is derived by theprocessing unit/DSP based on a signal to interference ratio of a commonpilot channel (CPICH).
 4. The method according to claim 2, wherein saiddetection threshold (τ, τ_(FAR)) is derived by the processing unit/DSPbased on a signal to interference ratio, where the interference isestimated on the basis of symbols of the received signal (y) that shouldbe zero.
 5. The method according to claim 4, wherein said detectionthreshold (τ_(FAR)) is derived by the processing unit/DSP based on afalse detection rate factor (/_(FAR)) and a standard deviation (δ₆₈)ofthe interference of the received signal (y).
 6. The method according toclaim 1, wherein said one or more weight factors (x₁, . . . , x_(J);Ĉ_(j)) are derived by the processing unit/DSP on the basis of a signalto interference ratio (SIR) calculated for a common pilot channel(CPICH).
 7. The method according to claim 6, wherein said signal tointerference ratio (SIR) calculated for a common pilot channel (CPICH)is dependent on an estimate of the interference (N_(f) ^((j))) for agiven finger (f) of a RAKE receiver and a given group (j), where saidmethod further comprising: averaging the estimate of the interference(N_(f) ^((j))) over a predetermined number of groups before derivingsaid one or more weight factors (x₁, . . . , x_(J); Ĉ_(j)) on the basisof the signal to interference ratio (SIR) calculated for the commonpilot channel (CPICH).
 8. The method according to claim 1, wherein saidfirst signal is an acquisition indicator channel (AICH) signal or acollision detection/channel assignment indicator channel (CD/CA-ICH). 9.The method according to claim 1, wherein said received signal (y) is anestimated signal (Σ_(f=1) ^(F)y_(k,f) ^((AICH))w_(k,f)) derived on abasis of one or more weighted channel estimates (w_(k,f)) and ofde-spread symbols (y_(k,f) ^((AICH))) from a RAKE, wherein the one ormore weighted channel estimates (w_(k,f)) are based on a common pilotchannel (CPICH).
 10. The method according to claim 1, wherein saidreceived signal (y) comprises two or three signal groups and that thepattern (ŝ) comprises at least two or three pattern groups.
 11. Themethod of claim 1, wherein the method is embodied in computer codestored on a computer readable medium executed by a processor.
 12. Adevice for detecting a first signal in a received signal (y) using apattern (ŝ), the received signal (y) comprising at least one signalgroup (y⁽¹⁾, . . . , y^((J))), each signal group comprising a number (K)of signal symbols, the pattern (ŝ) comprising at least one pattern group(ŝ⁽¹⁾, . . . , ŝ^((J))), each pattern group comprising at least a number(K) of pattern symbols, the device comprises: means adapted to for eachof said at least one signal group (y⁽¹⁾, . . . , y^((J))) to multiplyeach signal symbol with a corresponding pattern symbol of said at leastone pattern group (ŝ⁽¹⁾, . . . , ŝ^((J))) and to derive a sum (Σ₁, . . ., Σ_(J); A_(j)) of the products of the multiplication, means forapplying a weight factor (x₁, . . . , x_(J); Ĉ_(j)) of one or moreweight factors (x₁, . . . , x_(j); Ĉ_(j)) to each sum (Σ₁, . . . ,Σ_(J); A_(j)) giving a weighted sum (x₁Σ₁, . . . , x_(j)Σ_(J);A_(j)/Ĉ_(j)), where said one or more weight factors (x₁, . . . , x_(J);Ĉ_(j)) are selected to preserve an orthogonality relation of saidpattern symbols of the at least one pattern group, and means fordetermining if a signal is detected or not based on said one or moreweighted sums (x₁Σ₁, . . . , x_(j)Σ_(J); A_(j)/Ĉ_(j)).
 13. The deviceaccording to claim 12, wherein said means for determining if a signal isdetected or not further comprises: a summation circuit for adding saidone or more weighted sums (x₁Σ₁, . . . , x_(j)Σ_(J); A_(j)/Ĉ_(j)) givinga first result (x₁Σ₁,+ . . . , +x_(j)Σ_(J); Σ_(j=1) ^(J)CA_(j)/Ĉ_(j));and detection means for comparing said first result with a detectionthreshold (τ, τ_(FAR)) in order to determine whether said signal isdetected or not.
 14. The device according to claim 13, wherein thedevice further comprises processing means for deriving said detectionthreshold (τ, τ_(FAR)) based on a signal to interference ratio of acommon pilot channel (CPICH).
 15. The device according to claim 13,wherein said device further comprises processing means for deriving saiddetection threshold (τ, τ_(FAR)) on the basis of a signal tointerference ratio and for estimating the interference on the basis ofsymbols of the received signal (y) that should be zero.
 16. The deviceaccording to claim 15, wherein the device further comprises processingmeans for deriving said detection threshold (τ, τ_(FAR)) based on afalse detection rate factor (/_(FAR)) and a standard deviation (δ_(ε))of the interference of the received signal (y).
 17. The device accordingto claim 12, wherein the device further comprises processing means forderiving one or more weight factors (x₁, . . . , x_(J); Ĉ_(j)) on thebasis of a signal to interference ratio (SIR) calculated for a commonpilot channel (CPICH).
 18. The device according to claim 17, whereinsaid signal to interference ratio (SIR) calculated for a common pilotchannel (CPICH) is dependent on an estimate of the interference (N_(f)^((j))) for a given finger (f) and a given group (j), where saidprocessing means is further adapted to: average the estimate of theinterference (N_(f) ^((j))) over a predetermined number of groups beforederiving said one or more weight factors (x₁, . . . , x_(J); Ĉ_(j)) onthe basis of the signal to interference ratio (SIR) calculated for thecommon pilot channel (CPICH).
 19. The device according to claim 12,wherein said first signal is an acquisition indicator channel (AICH)signal or a collision detection/channel assignment indicator channel(CD/CA-ICH).
 20. The device according to claim 12, wherein the devicefurther comprises a combiner circuit for deriving said received signal(y) as an estimated signal (Σ_(f=1) ^(F)y_(k,f) ^((AICH))w_(k,f))derived on the basis of one or more weighted channel estimates (w_(k,f))and of de-spread symbols (y_(k,f) ^((AICH))) from a RAKE, wherein theone or more weighted channel estimates (w_(k,f)) is based on a commonpilot channel (CPICH).
 21. The device according to claim 12, whereinsaid received signal (y) comprises two or three signal groups and thatthe pattern (ŝ) comprises at least two or three pattern groups.